Both buyers and sellers of livestock manure can realize its many benefits, and proper testing can help pinpoint its real fertilizer value, says Joel DeJong, Iowa State University (ISU) Extension field agronomist. “You wouldn’t go to buy commercial fertilizer and say, ‘just give me fertilizer.’ The nutrients in animal manure should be managed with the same care as commercial fertilizer,” he states.
DeJong tells producers it is important to determine the total amount of nutrients in the manure, the availability of those nutrients to the crop being grown, and the amount of nutrients needed to optimize crop yields.
Producers should have a representative sample of manure chemically analyzed to determine the nutrient value prior to applying it to the field, he suggests. He uses a 1,250-head finishing unit as an example: “If you have 500,000 gal. of manure with a chemical analysis of 50 lb. of nitrogen, 35 lb. of phosphorus, and 30 lb. of potassium per 1,000 gal. of manure, and estimating nitrogen values of $0.65/lb., phosphorus values of $1.20/lb. and potassium at $0.73/lb., you would have around $50,960 in value,” DeJong explains. Information about accurately sampling manure for nutrient analysis can be found at extension.iastate.edu.
Proper calibration of equipment will help ensure uniform application and improve the crop’s ability to utilize the manure nutrients. Kris Kohl, ISU Extension field engineer, explains one method of calibrating solid manure spreaders by using 1/2000th of an acre piece of plastic, which measures 5 ft. x 4 ft. 4 in. Spread the plastic on the ground in various locations from the beginning to the end of the field and collect the manure as it is spread on this area. By weighing the manure that is collected on the plastic (in pounds) a producer will be able to calculate the tons per acre being applied.
“If I pick up 20 lb. of manure on the plastic, I have a 20-ton application rate, for example,” Kohl says. “I also like being able to collect a manure sample off of the plastic to send to the lab to see what was actually land applied.” Additional information about calibration and uniformity of solid manure spreaders is available online in an ISU publication.
When applying liquid manure, Kohl reminds producers that manufacturing variations, manure foaming and solids build-up could mean the tank may not be filled at the rated capacity. These inconsistencies could result in over-or under-application, and the inaccuracies could affect crop yields and the environment. He recommends that producers measure the density of manure and the application spread pattern. Kohl also advocates weighing the tank, tires and hitch when the tank is empty and when it is full. “Often we will transfer 5,000 to 8,000 lb. of the weight on a liquid tank onto the hitch,” he says. Iowa State University offers a detailed explanation about weighing liquid manure tanks and determining application rates, in addition to providing a helpful worksheet online.
Both Kohl and DeJong recommend producers visit the Iowa Manure Management Action Group (IMMAG) Web page for additional manure management information.